There have been many recent attempts to write small structures at the nano-scale using a STM by various methods, some of which involve manipulating single atoms on the surface of metal or doped semiconductor surfaces. A general review is given in "Atomic and Molecular Manipulation with the Scanning Tunneling Microscope" J. A. Stroscio and D. M. Eigler Science Volume 254, 29 November 1991, p. 1319-1326. However, the structures so far reported have been non-conductive and serve only as a demonstration of the possibilities of the technique. In our GB application No. 9213054.1 filed on 16th June 1992, in contrast to the aforementioned prior art techniques, it is proposed to form nanofabricated structures which are conductive.
A problem with the STM is that when a nano-scale structure is formed on a substrate of the surface e.g. by manipulation of atoms with the probe tip, it necessary for the substrate to exhibit low resistivity in order to permit tunnel current feedback to be established between the probe tip and the substrate. Thus, if an electroconductive nano-scale structure formed on the substrate, its conductivity characteristics merge into the background of conductive substrate and accordingly, it is difficult to test or make use of the conductivity characteristics of the nano-structure on the substrate, particularly when it is intended to be used at room temperature.
With a view to overcoming this problem, the present invention provides a method of forming a nano-scale electro-conductive structure wherein a probe is used to produce a desired configuration of matter on a substrate, including causing the substrate to change from a relatively low to a relatively high conductivity condition, producing with the probe said desired configuration of matter on the substrate while in said relatively high conductivity condition, and thereafter causing the substrate to assume said relatively low conductivity condition, wherein said substrate assumes said relatively low conductivity condition at room temperature, and is heated to a temperature in excess of room temperature to achieve said relatively high conductivity condition during which said structure is formed with said probe.
Another problem encountered when constructing such nanoscale devices on a substrate is that it is difficult to form a device such that it is coupled to external connections on the substrate.